1. Technical Field
The present invention relates to a vertical-cavity surface-emitting laser diode (hereinafter referred to as VCSELs) device used as a light source of optical data processing or high-speed optical communication, and more specifically to a technology of compensating for temperature characteristics of a laser element.
2. Related Art
In technical fields such as optical communication or optical storage, there has been a growing interest in VCSELs. VCSELs have excellent characteristics which edge-emitting semiconductor lasers do not have. For example, VCSELs feature lower threshold current and smaller power consumption. With a VCSEL, a round light spot can be easily obtained. Also, evaluation can be performed while VCSELs are on a wafer, and light sources can be arranged in two-dimensional arrays. With these characteristics, demands especially as light sources in the communication field have been expected to grow.
It is known that VCSELs have a property in which its output varies in accordance with temperature variations when operated at a constant current. When the temperature of a VCSEL increases, optical output decreases, while when the temperature decreases, optical output increases. In a case where a VCSEL is used for a light source in the communication field, for example, in order to avoid communication errors or the like, optical output more than a certain amount is required. On the other hand, the optical output should be restricted to lower than a certain amount in terms of high frequency characteristics or eye-safe, for example. Therefore, variations in optical output due to temperature variations of a VCSEL are restricted by an APC (auto power control) circuit that controls current to be injected into the laser. The APC circuit monitors optical output of the VCSEL, and provides feedback to control drive current in order to keep the optical output constant.
When the increase in optical output due to a low temperature VCSEL is restricted by reducing current by an APC method, the value of current becomes lower than a range that has high frequency characteristics, and thus high-speed response is inhibited. Therefore, for a communication laser, a temperature-controlling device is provided to limit variations in temperature of the laser. However, there has been a problem in that the temperature-controlling device requires a temperature sensor for detecting temperatures, a piezo element, and a voltage controller that controls voltage to be applied to the piezo element. These components increase the cost of a light-emitting element module.